Flotation of magnesite and the like magnesium ores



Patented Apr.v 28, 1942 FLOTA'I ION F MAGNESITE AND LIKE MAGNESIUM OBES Arthur W. Fahrenwald, Moscow, Idaho, asslgnor to Northwest Magneslte Company, Chewclah, Wash, a corporation of Washington No Drawing. Application April 16, 1941, I Serial No. 888,881

2 Claims.

This invention relates to the beneflciation of magnesium ores, particularly magnesite, by froth flotation methods, and more particularly to the production of magnesite of high quality for the making of refractory shapes.

' The principal magnesium ores, such as magneslte and brucite, contain gangue material which may, andcommonly does reduce their value or applicability to many of the uses to which they are put, as for producing metallic magnesium or the highest quality refractory articles.

Experience in the manufacture of magnesite refractories has shown that the refractoriness of the products is governed largely by the percentages .of lime and silica, which are the major impurities in most magnesites. They form, together or in combination with minor impurities such as alumina, alkalies, and iron oxide, mixtures which melt, wholly or partly, at temperatures that are relatively low for refractory purposes. Thus, eutectics in the system A12O3 -CaOSiO2 melt at temperatures that are extremely low in comparison with the melting point of pure magnesia, e. g., in some instances as low as 1165" C. The phase equilibrium data show that the ratios of these three oxides in magnesites are generally such that in most cases they will be completelyliquid at 1600 C. The presence of these low melting silicates provides an amount of fluid glass which acts as a slippery, or lubricating, fluid that allows the magnesite grains to slip over each other. i

The softening consequent upon suchphenomena is.responsible for the pyro-plastic properties which make magnesite so desirable for making monolithic furnace bottoms. Thus, in the open hearth the softening allows the material to. yield under the weight of the metal and to heal cracks varying from about 1.5 to 2.3 per cent. Magnesites used for making bricks of average quality contain, in comparison, from about 1.4 to 1.9 per cent of CaO, 1.2 to 2.1 per cent of S102, and a total CaO-plus-SiO: content of about 3.1 to 3.5 per cent. And magnesites containing from 2.7 to 3.5 per cent of CaO and 2.4 to 2.6 per cent of SiOa, with a combined content of 5.1 to 6.1 per cent, can not be used alone for making brick of satisfactory refractory properties; these may be used for making furnace bottoms or they may be mixed with the highest quality magnesites for making brick of average quality.

Magnesite is one of the key' industrial materials because lack of sufficient supplies of good quality magnesite may seriously interfere with steel production and other operations requiring highly refractory basic refractories. Although there are extensive deposits of that mineral in this country, their nature and pre-existing methods of beneflciation are such that at the present time this country is ill-prepared to rely on domestic magnesite as the sole source of grades for making high quality bricks.

Up' to the present time the practice in this country has been to work only deposits of relatively high grade ore, and to hand-sort ore to select grades appropriate for various uses. Such methods are, of course, unsatisfactory because in hand-sorting reliance is placed largely upon the appearance of the ore and the skill and judgment of the picker. not be a reliable criterion of its purity or of the particular gangue material present, and however skilled a picker may be the ore may be of unsuitable quality because of the inability to distinguish and discard material containing an objectionable amount of gangue. This practice has been followed, however, because there has been available no means of satisfactorily and economically beneficiating these ores. In consequence of this situation the bulk of domestic magnesite produced is generally of the third type identified above, and not only do large reserves of lower grade ores remain unworked, but also there have accumulated tailing dumps which contain large quantities of magnesite unsuited for important uses but which could be used to advantage if a satisfactory beneficiating procedure were available.

Various modes of mechanically beneficiating magnesite have been proposed but of the flotation procedures suggested or tried up to the time of this invention none has been.so far as I am aware. wholly satisfactory. Thus, no processapplying ordinary one-stage flotation has been devised The appearance of the ore may whereby a magnesite concentrate of sufficiently high grade and merchantable quality can be produced regularly and reliably, and which is economically acceptable and applicable to ores of varying grades. For instance, although thefiotation of magnesite can be effected, difficulties have been encountered in effecting adequate separation between the magnesite and the various gangue materials, or in doing so economical-, ly. These difficulties apply not only to procedures in which the gangueis carried off in the froth, but also to those in which the gangue remains as a tailing- It has been proposed also to use two-stage flotation, as by floating gangue in one step, leaving a magnesite concentrate: which .is in turn floated and separated from a further amount of gangue, or to float magnesite from a portion of the gangue and then make a further separation in a second flotation stage. Such procedures have not found favor, however, either because they are not effective or because the reagents necessary are so expensive as to render the processes unattractive.

It is among the objects of this invention to provide a process for satisfactorily and economically beneflciating magnesium ores, especially magnesites, by separation of gangue to an extent such as to supply ore of improved quality, and which is simple, easily practiced with standard and readily available equipment, and is applicable generally to ores of this class.

, A further object of the invention is to provide an improved froth flotation process of beneficiating magnesium ores with attainment of the fore-v magnesite as quarried, and permits the production of magnesite of useful quality from magnesite wastes which have heretofore been not generally applicable'to commercial uses.

Yet another object is to provide a two-stage froth flotation process of beneficiating magnesite that is eflicient and economical.

Other objects will appear from the following description.

. -The invention will be described with particular reference to magnesite for ease of reference. The invention is predicated upon my discovery that excellent beneficiation of magnesite may be attained by subjecting it to a two-stage froth flotion treatment in which gangue matter, particularly siliceous and calcareous gangue, is first floated with a non-cationic collector, thus leaving hand-picking and the like grading operations.

More in detail, a suitable pulp of the ore is prepared containing I a non-cationic collector of silicates which after conditioning if necessary or desirable, is subjected to froth flotation with removal of the froth, which carries a substantial proportion of gangue matter, largely siliceous and calcareous gangue. The silicate-impoverished magnesite concentrate resulting from that operation is then subjected to further froth flotation in the presence of a collector of magnesite, and most suitably in the presence of adepressant of residual carbonate and siliceous gangue, whereby the magnesite carried oil in the froth is separated from a further amount of gangue matter. This froth is removed and from it there is recovered magnesite low in CaO and Si02, even to the point where it may be used for making the highest quality of magnesite brick.

Various non-cationic collectors of gangue presv ent in magnesite may be used in the first step of the process. I have discovered, however, that especially good results are to be had by the use of methyl amyl alcohol as a collector of this type,

not only because it is eflicientjn very low concentrations and is relatively cheap, but also because it exerts sufliciently good selective action by itself, i. e., without any other collector, frother or conditioner being necessary in this step. Thus, using methyl amyl alcohol in this manner there was floated from magnesite of a quality unsuited for making refractories a silica concentrate containing 18.8 per cent of S102 and 1.6 per cent of CaO using only 0.036 pound of' the collector per ton of magnesite. Larger proportions of collector did not substantially alter that result. A characteristic of methyl amyl alcohol is that the concentrate floated is higher in silica, but of about the same lime content, than concentrates produced by the more expensive cationic collectors.

Moreover, the froths produced by methyl amyl alcohol are better than obtain with cationic collectors.

A number of collectors for magnesite are similarlyknown but for most purposes I prefer to use a fatty acid, most suitably oleic acid, or a fatty acid derivative, such as fatty acid soaps, although other magnesite collectors of the anionic type, of which a large number are availab1e,might be used. Thus, tall oil-(talloel) and products made from it, and others are known. In general, no frother is needed in the second, or magnesite flotation,

I stage of the process, at least where oleic acid is tion procedures. The ore is ground to a degree of used as the collecting agent.

For most purposes the best separation of the magnesite from the gangue matter in the'second stage is to be had by theme of gangue depressors. Satisfactory results are to be had by the use of soluble silicates, suitably sodium disilicate, which act satisfactorily for depression of residual silicates in this stage of the process although other depressors, such as sodium phophate and others known in the art, may be used. Also,,tannic acid and its derivatives may be used as depressors of gangue, particularly calcite and dolomite (carbonates), and may advantageously be used to supplement the action of, for example, sodium silicate to produce magnesite very low in lime.

The practice of the invention follows generally that well known and understood for froth flotasub-division which physically frees the minerals suitable for forming a pulp or slurry. The gangue collector, e. g., methyl amyl alcohol, is then added, and the pulp is subjected to froth flotation. The froth containing gangue-rich material is removed, and the resultant magnesite concentrate is then treated with a depressor of siliceous matter, such as sodium disilicate, and magnesite collector, and with a further depressor such as tannic acid if necessary, and is further subjected to froth flotation, most suitably in a separate cell or other flotation apparatus, to form a froth containing magneslte concentrate separated from a further amount of gangue matter. The froth is removed in accordance with standard practice and the beneficiated magnesite removed from it.

As is understood in the art, the exact degree of subdivision of the ore will depend in part upon upon the particular gangue materials present, the

condition of the pulp, the particular reagents used, and the degree of beneficlation needed. As is understood, however, very small amounts of reagents suffice, and this aspect of the invention will be understood from the following examples.

EXAIWPLEI In one test there was used a magnestie containing silicate gangue equivalent to 3.56 per cent of S102, and carbonate gangue equivalent to 2.36 per cent ofCaO. This was subjected to froth fiotation with 0.06 pound per ton of methyl amyl alcohol. The concentrate of siliceous gangue removed in the froth contained silica and silicates equivalent to 12.86 per cent of S102, and carbonate gangue equivalent to 1.93 per cent of CaO. The resultant'magnesite concentrate was then subjected to froth flotation using, per ton, 0.8 pound of oleic acid, 0.7 pound of sodium disilicate, and 1.0 pound of a tannic acid derivative sold under the trade name 5-36.

per cent of S102 and 0.15 per cent of CaO. This shows the desirability of using tannic' acid in I combination with another depressor to produce magneslte very low in lime, as well as the very high quality with respect to silica.

EXAMPLE 2 S10, CaO

Percent Peroen H 3.56 2.36 1st fii geoncentrate 14.06 2.11 Mai er:

1001 concentrate 1.30 1.03

As further exempmnnz the benefits r the in- The mag' nesite'concentrate produced contained only 1.38

' vention, low grade inagnesite was subjected to flotation using in the first stage of each test 0048' pound per ton of methyl amyl alcohol. The magnesite concentrates produced were then 'sub- I jected to flotation with oleic acid as the magnesite collector, and with a gangue depressor. The results are givenin the following tables:

'I'AILI I Silicate concentrate Percent Prmml 18. ti 1. l

TABLI Maynesite concentrates from tests of Table I subjected to mdanesite flotation with reagents as shown:

Reagents Magnesito concentrate Test No.

Olelc Bodlum Tannlc acid disillcete acid 0&0

Pound: Pounds Pounds per ton pcrton Percent Percent 'I-'he foregoing tests make it clear that by the practice of the invention there is readily and economically produced magnesite adapted for use in producing high quality refractories, as is evident from the low contents of silicla and lime which are the key impurities with respect to refractory quality of this material.

According to the provisions of the patent statutes, I have explained the principle and method of practicing my invention and have described what I now consider to represent its best em- ,bodiments. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

1. In a two-stage froth flotation method of beneficiatlng a magnesium orein which siliceous gangue is removed from the orein the first stage, and magnesium ore is floated from a further amount of gangue in the secondstage, the improvement in said first stage which consists in subjecting the ore to flotation with methyl amyl 2. A' method according to claim 1 in which said methyl amyl alcohol is the in said first 8138.88.

ARTHUR w. FAHRENWALD.

sole collector used alcohol as a collector of siliceous gangue to float. 

